Plants which have pure air spaces make high demands on the purity of the interior air. Air cleaned of dust and microorganisms is necessary in the plants in order to maintain the desired air purity. In addition to filter pads and pocket filters, cartridge filters are a common component in air filters. Cartridge filters have a folded package which is aligned perpendicularly to the flow direction and an outer frame. The folded package and the frame are sealed against one another using a sealing material. The folded packages are formed using fanfolded filter paper. In air filters for suspended matter, synthetic materials which can be processed in liquid form are exclusively used as sealing material. A nonwoven filter may also be placed into fine filters as sealing material.
The outer frame lends the filter the necessary mechanical stability, protects the filter package from damage, and allows for tightly fitting the filter element into a receptacle. Wood, sheet metal, or extruded aluminum sections are used as frame material. In framing of cartridge filters using a seal made of synthetic material processed in liquid form, the four frame parts are simultaneously joined perpendicularly to one another and bonded with the folded package. The advantage of this technique is in the fact that no additional casting molds or a specific configuration of the frame parts are necessary. However, the disadvantage is that the synthetic material used for the seal is not completely liquid so that the folded package occasionally does not penetrate the synthetic material at all points, thus creating leaks.
A different possibility for manufacturing the cartridge filter includes pouring a liquid casting compound into a prepared casting mold which represents one side of the frame and subsequently setting the folded package into the liquid. After curing of the casting compound, the step is repeated for the other sides of the folded package. Using this technique, the folded package always penetrates the liquid synthetic material completely, so that leaks are prevented. Since a liquid synthetic material is cast, the frame part itself must be formed as a casting mold, or additional auxiliary devices are necessary to prevent the sealing means from running. During joining, for example, additional bars are attached to the frame part as casting edges which prevent the casting compound from running. After curing of the casting compound, these auxiliary devices are again removed. Since the marketplace demands cartridge filters in almost any dimension, separate equipment is required for the production of each frame. By using wood frames or even deep-drawn or cast frame parts, the variety of models can only be satisfied very expensively since each dimension requires a separate deep-draw tool, for example.